LiFePO4 precursor for manufacturing electrode material of Li-ion battery and method for manufacturing the same

ABSTRACT

An LiFePO4 precursor for manufacturing an electrode material of an Li-ion battery and a method for manufacturing the same are disclosed. The LiFePO4 precursor of the present disclosure can be represented by the following formula (I):LiFe(1-a)MaPO4  (I)wherein M and a are defined in the specification, the LiFePO4 precursor does not have an olivine structure, and the LiFePO4 precursor is powders constituted by plural flakes.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) of U.S. patent application for “LiFePO₄ flakes for Li-ion battery and method for manufacturing the same”, U.S. application Ser. No. 15/152,023 filed May 11, 2016, and the subject matter of which is incorporated herein by reference.

U.S. application Ser. No. 15/152,023 filed May 11, 2016 is a divisional application of U.S. application Ser. No. 13/529,221 filed Jun. 21, 2012 which claims the benefits of the Taiwan Patent Application Serial Number 100121791, filed on Jun. 22, 2011, the subject matter of which is incorporated herein by reference.

BACKGROUND 1. Field

The present disclosure relates to a LiFePO₄ precursor for manufacturing an electrode material of an Li-ion battery and a method for manufacturing the same. More specifically, the present disclosure provides a novel LiFePO₄ precursor for manufacturing an electrode material of an Li-ion battery and a method for manufacturing the same.

2. Description of Related Art

As the development of various portable electronic devices continues, more and more attention focuses on the techniques of energy storage, and batteries are the main power supplies for these portable electronic devices.

Among commercial batteries, small-sized secondary batteries are especially the major power supplies for portable electronic devices such as cell phones and notebooks. In addition, secondary batteries are applied to not only portable electronic devices, but also electric vehicles.

Among the developed secondary batteries, the lithium secondary batteries (also named as the Li-ion batteries) developed in 1990 are the most popular batteries used nowadays. The cathode material of the initial lithium secondary batteries is LiCoO₂. LiCoO₂ has the properties of high working voltage and stable charging and discharging voltage, so the secondary batteries which use LiCoO₂ as a cathode material are widely applied to portable electronic devices. Then, LiFePO₄ with an olivine structure and LiMn₂O₄ with a spinal structure were also developed as a cathode material for lithium secondary batteries. Compared to LiCoO₂, the safety of the batteries can be improved, the charge/discharge cycles can be increased, and the cost can be further reduced when LiFePO4 or LiMn₂O₄ is used as cathode material of secondary batteries.

Although the batteries which use LiMn₂O₄ as cathode materials have low cost and improved safety, the spinal structure of LiMn₂O₄ may collapse during the deep discharge process, due to Jahn-Teller effect. In this case, the cycle performance of the batteries may further degrade. When LiFePO₄ is used as cathode material of batteries, the batteries also have the properties of low cost and further improved safety. In addition, the capacity of LiFePO₄ is higher than that of LiMn₂O₄, so the batteries made from LiFePO₄ can further be applied to devices, which need large current and high power. Furthermore, LiFePO₄ is a non-toxic and environmentally friendly material, and also has great high temperature characteristics. Hence, LiFePO₄ is considered as an excellent cathode material for lithium batteries. Currently, the average discharge voltage of the lithium batteries using LiFePO₄ as a cathode material is 3.2˜3.4 V vs. Li⁺/Li.

A conventional structure of the Li-ion batteries comprises: a cathode, an anode, a separator, and a Li-containing electrolyte. The batteries perform the charge/discharge cycles by the lithium insertion and extraction mechanism, which is represented by the following equations (I) and (II). Charge: LiFePO₄ −xLi⁺ −xe ⁻ →xFePO₄+(1−x)LiFePO₄  (I) Discharge: FePO₄ +xLi⁺ +xe ⁻ →xLiFePO₄+(1−x)FePO₄  (II)

When a charge process of the batteries is performed, Li ions extract from the structure of LiFePO₄; and the Li ions insert into the structure of FePO₄ when a discharge process is performed. Hence, the charge/discharge process of the Li-ion batteries is a two-phase process of LiFePO₄/FePO₄. However, the diffusion rate of the Li ions in LiFePO₄ and FePO₄ is quite low, so some metal dopants may generally be added into the cathode materials to increase the diffusion rate of the Li ions. In addition, the Li-ion diffusion path of the currently used LiFePO₄ is long, so the conductivity of LiFePO₄ is not good enough. Hence, the LiFePO₄ powders may be coated with carbon to increase the conductivity of LiFePO₄ powders, in order to increase the charge/discharge efficiency of the batteries. However, the process for manufacturing LiFePO₄ powders becomes more complicated when the LiFePO₄ powders are doped with metal additives or coated with carbon. In this case, the cost of the batteries is also increased.

Currently, the LiFePO₄ powders are usually prepared by a solid-state process. However, the property of the product is highly related to the sintering temperature of the solid-state process. When the sintering temperature is below 700° C., all the raw materials have to be mixed well. If the raw materials are not mixed well, Fe³⁺ impurity phase will be present in the LiFePO₄ powders. When sintering temperature is below 600° C., the average grain size of the LiFePO₄ powders will be smaller than 30 μm. However, if the sintering temperature is increased, the average grain size of the LiFePO₄ powders will be larger than 30 μm. When the average grain size of the LiFePO₄ powders is larger than 30 μm, a grinding process and a sieving process have to be performed to obtain powders with grain size between 1 μm to 10 μm. Hence, it is difficult to prepare LiFePO₄ powders with nano-size by the use of the solid-state process.

Therefore, it is desirable to provide a method for manufacturing nano-sized cathode materials of Li-ion batteries in a simple way, in order to increase the charge/discharge efficiency of the batteries and reduce the cost thereof.

SUMMARY

An object of the present disclosure is to provide an LiFePO₄ precursor for manufacturing an electrode material of an Li-ion battery and a method for manufacturing the same.

The LiFePO₄ precursor for manufacturing an electrode material of an Li-ion battery of the present disclosure can be represented by the following formula (I): LiFe_((1-a))M_(a)PO₄  (I) wherein M comprises at least one metal selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Zr, Tc, Ru, Rh, Pd, Ag, Cd, Pt, Au, Al, Ga, In, Be, Mg, Ca, Sr, B, and Nb, 0≤a<0.5, the LiFePO₄ precursor does not have an olivine structure, and the LiFePO₄ precursor is powders constituted by plural flakes.

The method for manufacturing the aforesaid LiFePO₄ precursor of the present disclosure may comprise the following steps: providing a mixed organic solution, which comprises Li, Fe, and P, wherein the Li contained in the mixed organic solution is derived from a Li-containing precursor or a P and Li-containing precursor, the Fe contained in the mixed organic solution is derived from an Fe-containing precursor or a P and Fe-containing precursor, and the P contained in the mixed organic solution is derived from a P-containing precursor, a P and Li-containing precursor, or a P and Fe-containing precursor; and heating the mixed organic solution under reflux to a predetermined temperature and maintaining the predetermined temperature for a predetermined period to obtain the aforesaid LiFePO₄ precursor.

The present disclosure further provides a method for manufacturing an LiFePO₄ electrode material of an Li-ion battery, which comprises: providing the aforesaid LiFePO₄ precursor; and heat-treating the LiFePO₄ precursor to obtain the LiFePO₄ electrode material.

In the present disclosure, the precursors contained in the organic mixed solution are reacted with each other to form the LiFePO₄ precursor, which is a precursor for forming the LiFePO₄ electrode material of the Li-ion battery. Herein, the crystalline structure of the LiFePO₄ precursor of the present disclosure is different from that of the conventional LiFePO₄ powders used in the Li-ion battery. More specifically, the LiFePO₄ precursor of the present disclosure does not have an olivine structure.

In addition, when the LiFePO₄ precursor of the present disclosure is heat-treated, the LiFePO₄ electrode material of the Li-ion battery can be obtained. Herein, the shapes of the LiFePO₄ precursor can be maintained after the heat treatment, which means that the obtained LiFePO₄ electrode material have the same shapes as the LiFePO₄ precursor. In the present disclosure, the LiFePO₄ precursor is powders having flakes, so the obtained LiFePO₄ electrode material is also powders having flakes with thin thickness. Because the thickness of the obtained LiFePO₄ electrode material is very thin, the insertion and extraction path of the Li ions can be greatly shortened, and the diffusion rate of the Li ions can further be increased. When the obtained LiFePO₄ electrode material is used as cathode materials of the Li-ion battery, the charge-discharge efficiency of the Li-ion battery can be increased due to the short Li-ion diffusion path.

In the present disclosure, the LiFePO₄ precursor may comprise powders with different crystalline. In the present disclosure, the LiFePO₄ precursor may comprise an amorphous zone and a crystallized zone.

Herein, a content of the amorphous zone can be greater than a content of the crystallized zone. For example, a ratio of the content of the amorphous zone to the content of the crystallized zone can be ranged from 10:1 to 2:1, from 9:1 to 2:1, from 8:1 to 2:1, from 7:1 to 2:1, from 6:1 to 2:1, from 5:1 to 2:1, from 10:1 to 3:1, from 9:1 to 3:1, from 8:1 to 3:1, from 7:1 to 3:1, from 6:1 to 3:1, or from 5:1 to 3:1. In one embodiment of the present disclosure, the ratio is about 4:1, but the present disclosure is not limited thereto. In addition, the distribution of the amorphous zone and the crystallized zone in the LiFePO₄ precursor is not particularly limited. For example, several crystallized zones can be distributed among the amorphous zone.

In the present disclosure, the crystallized zone may comprise at least one selected from the group consisting of C₂H₄Li₄O₇P₂·H₂O, Fe₃H₉(PO₄)₆·6H₂O, Fe₂Fe(P₂O₇)₂, FeLiO₂, Li₂Fe₂O₄, FePO₄, C₆H₆FeO₈·2H₂O, FePO₄(H₂O)₂, Li₂O₂, Li, and Fe₂O(PO₄). In another embodiment of the present disclosure, the crystallized zone may further comprise at least one selected from the group consisting of Fe₃O₄, Fe₃PO₇, Fe₃Fe₄(PO₄)₆ and C₂HLiO₄·H₂O.

In the present disclosure, the LiFePO₄ precursor may show an X-ray diffraction pattern having characteristic peaks at near 2θ angles of 19.37°, 21.47°, 24.11°, 25.95°, 32.35°, 35°, 36.46°, and 43.83°. In another embodiment of the present disclosure, the LiFePO₄ precursor may show the X-ray diffraction pattern having further characteristic peaks at near 2θ angles of 18.3°, 28.91° and 30.05°. It should be noted that, the XRD pattern of the LiFePO₄ precursor of the present disclosure is different from that of the LiFePO₄ powders with the olivine structure.

In the present disclosure, the LiFePO₄ precursor powders having the flakes and the LiFePO₄ powders obtained by heat-treating the LiFePO₄ precursor powders may respectively have a diameter ranged from 800 nm to 5 μm. In addition, the LiFePO₄ precursor powders having the flakes and the LiFePO₄ powders obtained by heat-treating the LiFePO₄ precursor powders may respectively have plural flakes. Herein, a length of each of the flakes is not particularly limited. For example, the length of each of the flakes can be respectively ranged from 400 nm to 5000 nm, from 400 nm to 3000 nm, from 400 nm to 2000 nm, from 400 nm to 1500 nm, from 400 nm to 1300 nm, from 400 nm to 1100 nm, 600 nm to 5000 nm, from 600 nm to 3000 nm, from 600 nm to 2000 nm, from 600 nm to 1500 nm, from 600 nm to 1300 nm, from 600 nm to 1100 nm, 700 nm to 5000 nm, from 700 nm to 3000 nm, from 700 nm to 2000 nm, from 700 nm to 1500 nm, from 700 nm to 1300 nm, or from 700 nm to 1100 nm. In addition, a thickness of each of the flakes is also not particularly limited. For example, the thickness of each of the flakes can be respectively ranged from 1 nm to 50 nm, from 1 nm to 40 nm, from 1 nm to 30 nm, from 1 nm to 20 nm, from 1 nm to 15 nm, from 3 nm to 50 nm, from 3 nm to 40 nm, from 3 nm to 30 nm, from 3 nm to 20 nm, from 3 nm to 15 nm, from 4 nm to 50 nm, from 4 nm to 40 nm, from 4 nm to 30 nm, from 4 nm to 20 nm, from 4 nm to 15 nm, from 5 nm to 50 nm, from 5 nm to 40 nm, from 5 nm to 30 nm, from 5 nm to 20 nm, from 5 nm to 15 nm, or from 5 nm to 14 nm.

In the present disclosure, when the LiFePO₄ precursor powders and the LiFePO₄ powders obtained by heat-treating the LiFePO₄ precursor powders respectively have plural flakes, the flakes can be gathered to from a flower-like shape or laminated to form a shale-like shape. In addition, one end of one of the flakes may be connected to one end of another one of the flakes.

In the present disclosure, the method for manufacturing the LiFePO₄ precursor may further comprise a step of coating the LiFePO₄ precursor with a carbon source through a milling process to form a carbon layer on the powders. Thus, the LiFePO₄ precursor powders of the present disclosure may be further coated with a carbon layer. In addition, a catalyst may also be added in the step of coating the LiFePO₄ precursor with the carbon source through the milling process. The catalyst can be, for example, ferrocene; but the present disclosure is not limited thereto. Herein, the milling process can be a ball-milling process, but the present disclosure is not limited thereto. Herein, the examples of the carbon source are not particularly limited, and can be any sugar such as sucrose, stearic acid, citric acid, lauric acid, polystyrene, polystyrene ball (PS ball) or vitamin C (L-ascorbate). In addition, the addition amount of the carbon source can be 0.1-40 wt % of the weight of the LiFePO₄ precursor powders. In one embodiment of the present disclosure, the addition amount of the carbon source can be 2.5-30 wt % of the weight of the LiFePO₄ precursor powders. In another embodiment of the present disclosure, the addition amount of the carbon source can be 5-20 wt % of the weight of the LiFePO₄ precursor powders.

In the method of the present disclosure, a small amount of metal-containing compounds may be further added in the mixed organic solution, and the doped metal in the LiFePO₄ precursor can increase the conductivity of the LiFePO₄ powders obtained by heat-treating the LiFePO₄ precursor powders. Herein, the doped metal can be at least one selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Zr, Tc, Ru, Rh, Pd, Ag, Cd, Pt, Au, Al, Ga, In, Be, Mg, Ca, Sr, B, and Nb. In addition, the metal-containing compounds may be sulfates, carbonates, nitrates, oxalates, acetates, chlorites, bromides, or iodides of the aforementioned doped metals. In one embodiment of the present disclosure, the metal-containing compounds are sulfates of the aforementioned doped metals. In another embodiment of the present disclosure, the metal-containing compounds are sulfates of Mn, Cr, Co, Cu, Ni, Zn, Al, or Mg. Thus, in the present disclosure, M in the formula (I) can be selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Zr, Tc, Ru, Rh, Pd, Ag, Cd, Pt, Au, Al, Ga, In, Be, Mg, Ca, Sr, B, and Nb. In one embodiment of the present disclosure, M in the formula (I) can be one or more metals selected from the group consisting of Mn, Cr, Co, Cu, Ni, Zn, Al, and Mg. In another embodiment of the present disclosure, M in the formula (I) can be one or more metals selected from the group consisting of Mn, Cu, Zn, Al, Ni, and Mg.

In the method of the present disclosure, the Li-containing precursor can be at least one selected from the group consisting of LiOH, Li₂CO₃, LiNO₃, CH₃COOLi, Li₂C₂O₄, Li₂SO₄, LiCl, LiBr, and LiI; the Fe-containing precursor can be at least one selected from the group consisting of FeCl₂, FeBr₂, FeI₂, FeSO₄, (NH₄)₂Fe(SO₄)₂, Fe(NO₃)₂, FeC₂O₄, (CH₃COO)₂Fe, and FeCO₃; the P-containing precursor can be at least one selected from the group consisting of H₃PO₄, NaH₂PO₄, Na₂HPO₄, Mg₃(PO₄)₂, and NH₄H₂PO₄; the P and Li-containing precursor can be at least one selected from the group consisting of LiH₂PO₄, Li₂HPO₄, and Li₃PO₄; and the P and Fe-containing precursor can be at least one selected from the group consisting of Fe₃(PO₄)₂, and FePO₄. In addition, the mixed organic solution may not only contain the aforementioned precursors, but also may contain other additives such as surfactants, dispersants, polymer electrolytes, and stabilizers, which can facilitate the synthesis reaction or the dissolution of the precursors. Herein, the examples of the surfactants can be cetyltrimethylammonium bromide (CTAB), sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), or octyl phenol ethoxylate (Triton-X100); the examples of the dispersants can be potassium dodecyl sulfate, ammonium dodecyl sulfate, calcium dodecyl sulfate, sodium dodecyl sulfate, copper dodecyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl Sulfate, sodium dodecyl benzene sulfonate, magnesium dodecyl benzene sulfonate, sodium dodecyl sulfonate, magnesium dodecyl sulfonate, sodium decyl sulfonate, or sodium decyl sulfate; the examples of the polymer electrolytes can be polyvinylpyrollidone (PVP), peroxyacetic acid (PAA), polyethyleneimine (PEI), or polyacrylamide (PAM); and the examples of the stabilizers can be polyvinyl alcohol (PVA), or polyvinyl acetate (PVAc). The aforementioned additives can control the crystal size and the preferential growth direction of the powders. In addition, the aforementioned additives can be used alone or two or more additives can be used together.

In the method of the present disclosure, the organic solvent in the mixed organic solution is not particularly limited, and can be any polyol organic solvents. For example, the organic solvent can be at least one selected from the group consisting of ethylene glycol (EG), diethylene glycol (DEG), glycerol, triethylene glycol (TEG), tetraethylene glycol (TTEG), polyethylene glycol (PEG), Dimethyl sulfoxide (DMSO), and N,N-dimethylmethanamide (DMF). In one embodiment of the present disclosure, the organic solvent is DEG, glycerol, or a combination thereof.

In the method of the present disclosure, the mixed organic solution is heated under reflux to a predetermined temperature and the predetermined temperature is maintained for a predetermined period to perform the reaction for obtaining the aforesaid LiFePO₄ precursor. Herein, the predetermined temperature can be ranged from 105° C. to 350° C., from 105° C. to 300° C., from 105° C. to 280° C., from 105° C. to 250° C., from 200° C. to 350° C., from 200° C. to 300° C., from 200° C. to 280° C., from 200° C. to 250° C., from 220° C. to 350° C., from 220° C. to 300° C., from 220° C. to 280° C. or from 220° C. to 250° C. In one embodiment of the present disclosure, the predetermined temperature is about 220° C. In addition, the predetermined temperature is maintained for a predetermined period to perform the reaction for forming the aforesaid LiFePO₄ precursor. Herein, the predetermined period can be ranged from 2 hrs to 20 hrs, from 2 hrs to 15 hrs, from 2 hrs to 10 hrs, from 2 hrs to 8 hrs, from 2 hrs to 5 hrs, from 2 hrs to 3 hrs, from 3 hrs to 20 hrs, from 3 hrs to 15 hrs, from 3 hrs to 10 hrs, from 3 hrs to 8 hrs, or from 3 hrs to 5 hrs. The temperature may be slightly increased when undergoing the reaction for forming the aforesaid LiFePO₄ precursor.

Herein, the mixed organic solution can be heated under an atmosphere or with an introduced gas flow. The atmosphere or the introduced gas flow can be used as a protective gas or a reducing gas, which may comprise one selected from the group consisting of N₂, H₂, He, Ne, Ar, Kr, Xe, CO, methane, N₂—H₂ mixture, and a mixture thereof. In one embodiment of the present disclosure, the protective gas or the reducing gas is N₂, H₂, or N₂—H₂ mixture. In another embodiment of the present disclosure, the protective gas or the reducing gas is N₂—H₂ mixture.

In the present embodiment, the pressure for heating the mixed organic solution or for performing the reaction for forming the aforesaid LiFePO₄ precursor can be about atmospheric pressure. However, the conventional process for forming LiFePO₄ powders is usually held under high pressure, and the apparatus for performing the conventional process is more expensive or complicated than the method of the present disclosure.

In the method of the present disclosure, the LiFePO₄ precursor may be heat-treated under an atmosphere or with an introduced gas flow to obtain the LiFePO₄ electrode material. Herein, the atmosphere or the introduced gas flow can also be used as a protective gas or a reducing gas, which may comprise one selected from the group consisting of N₂, H₂, He, Ne, Ar, Kr, Xe, CO, methane, N₂—H₂ mixture, and a mixture thereof. In one embodiment of the present disclosure, the protective gas or the reducing gas is Ar, N₂, H₂, or N₂—H₂ mixture. In another embodiment of the present disclosure, the protective gas or the reducing gas is Ar, or N₂—H₂ mixture.

In the method of the present disclosure, the temperature for the heat treatment can be ranged from 300° C. to 1000° C., from 400° C. to 1000° C., from 500° C. to 1000° C., from 300° C. to 900° C., from 400° C. to 900° C., or from 500° C. to 900° C. In one embodiment of the present disclosure, the temperature for the heat treatment is ranged from 500° C. to 860° C. In addition, the time period for performing the heat treatment can be ranged from 2 hrs to 20 hrs, from 2 hrs to 15 hrs, from 2 hrs to 10 hrs, from 2 hrs to 8 hrs, from 2 hrs to 5 hrs, or from 2 hrs to 3 hrs.

In addition, the obtained LiFePO₄ powders of the present disclosure can be used as a cathode material to prepare a Li-ion battery, through any conventional method in the art. Here, the method for manufacturing the Li-ion battery is briefly described, but the present disclosure is not limited thereto.

An anode current collector is coated with a carbon material, and then the carbon material is dried and pressed to form an anode for the Li-ion battery. A cathode current collector is coated with a cathode active material (i.e. the LiFePO₄ powders of the present disclosure), and then the cathode active material is dried and pressed to form a cathode for the Li-ion battery. Next, a separator is inserted between the cathode and the anode, a Li-containing electrolyte is injected, and a Li-ion battery is obtained after packaging.

Other objects, advantages, and novel features of the disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XRD pattern of an LiFePO₄ precursor according to Example 1 of the present disclosure.

FIG. 2A to FIG. 2C shows TEM photos of one region of an LiFePO₄ precursor according to Example 1 of the present disclosure.

FIG. 3 is a TEM photo of another region of an LiFePO₄ precursor according to Example 1 of the present disclosure.

FIG. 4 is a TEM photo of further another region of an LiFePO₄ precursor according to Example 1 of the present disclosure.

FIG. 5A to FIG. 5F are SEM photos of an LiFePO₄ precursor according to Example 1 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

The following embodiments when read with the accompanying drawings are made to clearly exhibit the above-mentioned and other technical contents, features and/or effects of the present disclosure.

Through the exposition by means of the specific embodiments, people would further understand the technical means and effects the present disclosure adopts to achieve the above-indicated objectives. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present disclosure should be encompassed by the appended claims.

Furthermore, when a value is in a range from a first value to a second value, the value can be the first value, the second value, or another value between the first value and the second value.

Example 1 to Example 29

The LiFePO₄ precursors of Example (Ex as the abbreviation in the following Table 1) 1 to Example 29 are synthesized according to the following Table 1. In the following Table 1, the addition amounts and molar ratios of H₃PO₄, FeC₂O₄·2H₂O, and LiOH·H₂O, ambient temperature (Temp 1), relative humidity (RH), time for increasing to 220° C. (T1), reaction time (T2), final temperature after the reaction is stopped (Temp 2), and N₂ gas flow (N₂).

In Example 1 to Example 25, H₃PO₄ (2 g), FeC₂O₄·2H₂O (3.6 g), and LiOH·H₂O (0.84 g) were mixed in a ratio of 1:1:1, and dissolved in DEG (100 ml) to obtain a mixed organic solution (0.2 M). In Example 20 and Example 26, SDBS (0.02 mole) and SDS (0.01 mole) was also added respectively into the mixed organic solution. In Example 27, FeC₂O₄·2H₂O used in Example 1 was replaced by FeC₂O₄·H₂O:MnC₂O₄·2H₂O (9:1). In Example 28, FeC₂O₄·2H₂O used in Example 1 was replaced by FeC₂O₄·H₂O:NiC₂O₄·2H₂O (9:1). In Example 29, FeC₂O₄·2H₂O used in Example 1 was replaced by FeC₂O₄·H₂O:MnC₂O₄·2H₂O:NiC₂O₄·2H₂O (9:0.5:0.5). Next, the mixed organic solution was heated to 220° C. Then, N₂ gas was introduced, the mixed organic solution was reacted under reflux, at 220° C. for a period of time (T2). The reaction was performed under atmospheric pressure. After the mixed organic solution was filtrated, the LiFePO₄ precursor was obtained.

The obtained LiFePO₄ precursor was examined by an X-ray diffractometer (Shimadzu 6000) to obtain the crystal structure thereof. The X-ray diffraction pattern (XRD pattern) was obtained by applying Cu Ku radiation, the 2θ-scanning angle is ranged from 15° to 45°, and the scanning rate is 1°/min. The XRD pattern of the LiFePO₄ precursor of Example 1 is shown in FIG. 1.

The XRD pattern shown in FIG. 1 has characteristic peaks at near 2θ angles of 19.37° (peak 2), 21.47° (peak 4), 24.110 (peak 6), 25.95° (peak 7), 32.35° (peak 10), 35° (peak 11), 36.46° (peak 12), and 43.83° (peak 13). In addition, the XRD pattern shown in FIG. 1 further has characteristic peaks at near 2θ angles of 18.3° (peak 1), 28.91° (peak 8) and 30.05° (peak 9).

The XRD pattern is different from the XRD pattern of LiFePO₄ crystal with an olivine structure (JCPDS No. 81-1173). Thus, the LiFePO₄ precursor of the present disclosure does not have an olivine structure.

The LiFePO₄ precursors prepared in Examples 2 to Example 29 are also examined by an X-ray diffractometer, and the obtained XRD patterns are similar to that shown in FIG. 1, except that some peaks (especially, the peak 1 and the peak 8) are very week or not found in the XRD patterns of the LiFePO₄ precursors of some examples. The presences of the peak 1 and peak 8 are also listed in the following Table 1.

TABLE 1 Temp 1 RH Temp 2 N₂ Ex (° C.) (%) T1 T2 (° C.) (c.c./min) Peak 1 Peak 8 1 29 60 5 hr 29 min 3 hr 1 min 238 100+ V V 2 — — 8 hr 47 min 3 hr 24 min 237 100 V V 3 27 68 5 hr 44 min 3 hr 239 100+ V V 4 25 70 7 hr 12 min 3 hr 13 min 238 100+ V Δ 5 25 60 2 hr 57 min 3 hr 1 min 242 100+ V V 6 24 50 4 hr 43 min 3 hr 13 min 239 100+ V V 7 29 55 5 hr 30 min 3 hr 12 min 239 100+ V Δ 8 — — 4 hr 22 min 3 hr 236 100+ V V 9 — — 5 hr 15 min 3 hr 238 100+ Δ Δ 10 — — 6 hr 29 min 3 hr 2 min 236 100+ V Δ 11 — — 5 hr 44 min 3 hr 11 min 240 100+ V V 12 23 60 — — — 100+ V Δ 13 23 60 8 hr 9 min 3 hr 22 min 240 100 V V 14 23 60 8 hr 11 min 3 hr 6 min 235 100 V Δ 15 — — — — 241 100+ Δ Δ 16 25 70 4 hr 16 min 3 hr 4 min 234 100 X V 17 27 55 7 hr 37 min 3 hr 235 100 X Δ 18 25 65 8 hr 43 min 3 hr 234 100 X X 19 26 55 7 hr 2 min 3 hr 234 100 X X 20 23 60 15 hr 30 min 4 hr 19 min 240 100 X Δ 21 25 60 9 hr 46 min 5 hr 59 min 237 100 X X 22 27 70 10 hr 13 min 3 hr 235 100+ X X 23 — — 5 hr 25 min 5 hr 34 min 242 100+ X X 24 — — 4 hr 15 min 16 hr 23 min 243 100+ X X 25 29 65 8 hr 1 min 16 hr 241 100 X Δ 26 — — — 3 hr — 100 V Δ 27 — — — 3 hr — 100 X X 28 — — — 3 hr — 100 V V 29 — — — 3 hr — 100 V+ X V: Peak can be found. V+: Peak is very strong. Δ: Peak is very weak or almost disappears. X: Peak cannot be found. —: Not measured.

According to the data shown in Table 1, the presences of the peak 1 and peak 8 may not be related to the ambient temperature, relative humidity, time for increasing to 220° C., reaction time, final temperature, and N₂ gas flow. The intensity of the peaks (especially, the peak 1 and the peak 8) may be related to the compounds or the contents of the compounds existing in the LiFePO₄ precursors.

According to the XRD data (JCPDS card), it is found that the XRD pattern of the compound containing Li, Fe, P, O or H may have one peak with the strongest intensity. Herein, each peaks contributed by which crystallized compound are investigated by comparing the XRD pattern of FIG. 1 with JCPDS cards. The comparison results are listed in the following Table 2.

TABLE 2 Com- Com- pound 1 pound 2 Peak JCPDS Compound 1 JCPDS Compound 2 2θ No. Formula No. Formula Peak 1 74-1910 Fe₃O₄ — — 18.3° Magnetite Peak 2 46-1551 C₂H₄Li₄O₇P₂•H₂O 44-812  Fe₃H₉(PO₄)₆•6H₂O 19.37° Lithium hydroxyl Iron hydrogen ethyldiene phosphate hydrate phosphonate Peak 4 80-2315 Fe₂Fe(P₂O₇)₂ — — 21.47° Iron phosphate Peak 6 65-2754 FeLiO₂ 75-1603 Li₂Fe₂O₄ 24.11° Tetragonal Lithium iron(III) Lithium iron(III) oxide oxide Peak 7 72-2124 FePO₄ 33-1721 C₆H₆FeO₈•2H₂O 25.95° Iron(III) phosphate Iron hydrogen malonate dihydrate Peak 8 76-1761 Fe₃PO₇ 28.91° Triiron(III) trioxide phosphate(V) Peak 9 72-2446 Fe₃Fe₄(PO₄)₆ 49-1209 C₂HLiO₄•H₂O 30.05° Iron phosphate Lithium hydrogen oxalate hydrate Peak 10 72-464  FePO₄(H₂O)₂ 32.35° Phosphosiderite Peak 11 74-115  Li₂O₂ 35° Lithium peroxide Peak 12 89-4083 Li 36.46° Lithium Peak 13 48-582  Fe₂O(PO₄) 43.83° Alpha-iron oxide phosphate

In addition, the LiFePO₄ precursors obtained in Examples 1 to 29 were also examined by Inductively Coupled Plasma (ICP). The results show that the atomic ratio of Li, Fe and P was very close to 1:1:1 (i.e. Li:Fe:P=1:1:1) in the FePO₄ precursors obtained in Examples 1 to 29, which indicated that the LiFePO₄ precursors obtained in Examples 1 to 29 can be directly used to prepare the LiFePO₄ electrode material.

Example 30 to Example 35

In Example 30 to Example 35, the LiFePO₄ precursors prepared in Examples 4, 6, 3, 13, 9, and 14 were respectively coated with a carbon source through a milling process to form a carbon layer on the powders of the LiFePO₄ precursors. Briefly, a carbon source was dissolved in a milling solution, followed by mixing with the LiFePO₄ precursor. Then, zirconia balls were used and the milling process was held for 2 hrs to obtain the LiFePO₄ precursor with a carbon layer formed thereon. In Example 34, the milling solution with the carbon source (steric acid) was heated to well dissolve the steric acid.

The diameter of the used zirconia balls, the milling solution used in the milling process, the carbon source, and the weight ratio of the carbon source to the LiFePO₄ precursor are listed in the following Table 3. In addition, the obtained LiFePO₄ precursor coated with the carbon source was also examined by an X-ray diffractometer (Shimadzu 6000) to obtain the crystal structure thereof. The XRD patterns of the LiFePO₄ precursor with or without the carbon layer formed thereon were compared, and the comparison results are listed in the following Table 3.

TABLE 3 Carbon source & LiFePO₄ Milling weight Changes in the XRD Ex precursor Diameter solution ratio patterns 30 Example 4 0.8 mm   25 ml H₂O Sucrose Peak 1 disappeared 0.15 Peak 8 disappeared Peak 9 weakened 31 Example 6 0.8 mm   5 ml H₂O + Sucrose Peak 1 weakened 20 ml EtOH 0.15 Peak 8 disappeared Peak 9 weakened 32 Example 3 2 mm 25 ml H₂O Sucrose Peak 1 weakened 0.15 Peak 8 disappeared Peak 9 weakened 33 Example 2 mm 5 ml H₂O + Sucrose Peak 1 weakened 13 20 ml EtOH 0.15 Peak 8 disappeared Peak 9 weakened 34 Example 9 2 mm 30 ml EtOH Steric Peak 1 weakened acid Peak 8 disappeared 0.083 Peak 9 weakened 35 Example 2 mm 25 ml Poly- Peak 1 weakened 14 Toluene styrene Peak 8 disappeared 0.068 Peak 9 weakened

The results of Example 30 to Example 35 indicate that the crystalline of the LiFePO₄ precursor is decreased or the lattice of the crystals in the LiFePO₄ precursor is destroyed due to the milling process. In addition, in Example 32 to Example 35, after the milling process, the decreasing level of the intensity of the peak 9 in Example 32 is greater than that in Example 33, the decreasing level of the intensity of the peak 9 in Example 33 is greater than that in Example 34, and the decreasing level of the intensity of the peak 9 in Example 35 is very small. These results indicate that the decreasing level of the intensity of the peak 9 is related to the water content in the milling solution.

The shapes of the LiFePO₄ precursor prepared in Example 1 were also observed with a high resolution transmission electron microscope (TEM) (JEOL 2010). FIG. 2A to FIG. 2C show TEM photos of one region of an LiFePO₄ precursor according to Example 1 of the present disclosure.

It is found that 80% of the LiFePO₄ precursor is amorphous zones and 20% of the LiFePO₄ precursor is crystallized zones, and the crystallized zones are spread among the amorphous zones.

The left photo shown in FIG. 2A was observed at the magnification of 40,000×. The right photo shown in FIG. 2A is the circle region of the left photo, which is one flake of the LiFePO₄ precursor and was observed at the magnification of 200,000×. The photo shown in FIG. 2B was observed at the magnification of 600,000×, which shows that one flake of the LiFePO₄ precursor is formed by an amorphous zone and a crystallized zone. After measured by Gatan Microscopy Suite Software, the result shown in FIG. 2C shows that the d-spacing of the crystallized zone is 2.56 Å, which is consistent with the interplanar spacing of (1, 0, 1) planes of Li₂O₂(JCPDS No. 75-115). As shown in FIG. 1 and Table 2, the strongest peak of the LiFePO₄ precursor is the peak 11, which is contributed by crystallized Li₂O₂. The crystallized zone shown in FIG. 2B and FIG. 2C has good crystalline and this crystallized zone is identified as the crystallized Li₂O₂; thus, the strongest peak 11 should be contributed by the crystallized Li₂O₂

FIG. 3 is a TEM photo of another region an LiFePO₄ precursor according to Example 1 of the present disclosure, which was observed at the magnification of 500,000×. It is found that different fringes can be found in one flake of the LiFePO₄ precursor. As shown in FIG. 3, three zones indicated by A, B and C with different fringe directions can be found, and some zones without good crystalline may exist between the zones indicated by A, B and C. After measured by Gatan Microscopy Suite Software, in the zone A, the d-spacing of the crystallized zone is 2.465 Å, which is consistent with the interplanar spacing of (1, 1, 0) planes of Li (JCPDS No. 89-4083). In the zone B, the d-spacing of the crystallized zone is 2.72 Å, which is similar to the interplanar spacing of (1, 2, 2) planes of FePO₄(H₂O)₂ (JCPDS No. 72-464). In the zone C, the d-spacing of the crystallized zone is 2.06 Å, which is consistent with the interplanar spacing of (0, 3, 1) planes of Fe₂O(PO₄) (JCPDS No. 48-582). The crystallized zones A, B and C shown in FIG. 3 have good crystalline and these crystallized zones A, B and C are respectively identified as Li, the crystallized FePO₄(H₂O)₂ and the crystallized Fe₂O(PO₄); thus, the peaks 12, 10 and 13 should be respectively contributed by Li, the crystallized FePO₄(H₂O)₂ and the crystallized Fe₂O(PO₄).

FIG. 4 is a TEM photo of further another region of an LiFePO₄ precursor according to Example 1 of the present disclosure, which was observed at the magnification of 600,000×. It is found that different fringes can be found in one flake of the LiFePO₄ precursor. As shown in FIG. 4, three zones indicated by D, E and F with different fringe directions can be found, and some zones without good crystalline may exist between the zones indicated by D, E and F. After measured by Gatan Microscopy Suite Software, in the zone D, the d-spacing of the crystallized zone is 2.54 Å, which is consistent with the interplanar spacing of (1, 3, 2) planes of C₆H₆FeO₈·2H₂O (JCPDS No. 33-1721). In the zone E, the d-spacing of the crystallized zone is 3.07 Å, which is similar to the interplanar spacing of (0, 1, 2) planes of Fe₃PO₇ (JCPDS No. 76-1761). In the zone F, the d-spacing of the crystallized zone is 2.67 Å, which is consistent with the interplanar spacing of (2, 1, 1) planes of Fe₃Fe₄(PO₄)₆(JCPDS No. 72-2446). The crystallized zones D, E and F shown in FIG. 4 have good crystalline and these crystallized zones D, E and F are respectively identified as the crystallized C₆H₆FeO₈·2H₂O, the crystallized Fe₃PO₇ and the crystallized Fe₃Fe₄(PO₄)₆; thus, the peaks 7, 8 and 9 should be respectively contributed by the crystallized C₆H₆FeOs₈.2H₂O, the crystallized Fe₃PO₇ and the crystallized Fe₃Fe₄(PO₄)₆.

According to the results shown in FIG. 2A to FIG. 4, the LiFePO₄ precursor are powders comprising amorphous zones and crystallized zones contributed from different crystallized compounds. Thus, the powders of the LiFePO₄ precursor are constituted by different crystallized compounds. In particular, one flake of the powder of the LiFePO₄ precursor may be constituted by more than one crystallized compounds.

The shapes of the LiFePO₄ precursor prepared in Example 1 were also observed with a scanning electron microscope (SEM) (Hitachi S-4000). The results are shown in FIG. 5A to FIG. 5F.

FIG. 5A was observed at the magnification of 10,000×. It can be found that the LiFePO₄ precursor is a powder having flakes, and a diameter of the powder is about 5 μm. It can also be found that the powder have plural flakes, which are gathered to form a flower-like shape. FIG. 5B was observed at the magnification of 40,000×. It can be found that each flake has a length of about 700 nm to 1000 nm. FIG. 5C was observed at the magnification of 150,000×. It can be found that each flake has a width of about 5 nm to 14 nm.

In addition to the shapes shown in FIG. 5A to FIG. 5C, the powder of the LiFePO₄ precursor may have other shape, in which the flakes are laminated to form a shale-like shape. FIG. 5D was observed at the magnification of 10,000×, which shows that some flakes are gathered to form a flower-like shape and some flakes are laminated to form a shale-like shape. FIG. 5E was observed at the magnification of 80,000×. It can be found that the gaps are present between flakes to form the shale-like shape.

FIG. 5F was observed at the magnification of 150,000×. It can be found that each flake has a thickness of about 5 nm to 10 nm. Thus, the flakes of the powders of the LiFePO₄ precursor have similar thicknesses despite the shapes of the powders.

According to the results shown in FIG. 5A to FIG. 5G, the LiFePO₄ precursor is a powder constituted with flakes. When the LiFePO₄ precursor of the present disclosure is heat-treated to form LiFePO₄, the obtained LiFePO₄ powder can also be a powder constituted with flakes. Thus, Li ions can extract from the powders in a uniform and high-density manner, so the current density of the Li-ion batteries can be further increased.

Example 36 to Example 43

H₃PO₄, FeC₂O₄, and LiOH were mixed in a ratio of 1:1:1, and dissolved in DEG to obtain a mixed organic solution. Next, the mixed organic solution was heated to 220° C. Then, N₂ gas was introduced, the mixed organic solution was reacted under reflux, at 220° C. for 3 hrs. After the mixed organic solution was filtrated, synthetic powders were obtained.

The synthetic powders were washed with DI water for three times, followed by dried at 55° C. to obtain the LiFePO₄ precursors.

The obtained LiFePO₄ precursors were respectively mixed with sucrose (15 wt %), and the mixtures were mixed by using a 3D mixer for 2 hrs to obtain mixing powders.

The mixing powders were placed in a vacuum heat treatment furnace introduced with N₂ gas or a heat treatment furnace introduced with N₂ constant airflow, and the heat treatment was held at 750° C. for 2 hrs. Then, LiFePO₄ powders for an electrode material were obtained.

The LiFePO₄ precursors prepared in Examples 36 to Example 43 were also examined by an X-ray diffractometer, and the obtained XRD patterns are similar to that shown in FIG. 1. Herein, only the peak 1 and the peak 8 are listed in the following Table 4.

In addition, the shapes of the LiFePO₄ precursors and LiFePO₄ powders prepared in Example 36 to Example 43 were also observed with a scanning electron microscope (SEM) (Hitachi S-4000). The results are summarized in the following Table 4.

TABLE 4 Concentration XRD features of Shapes of the Shapes of the DEG of the mixed the LiFePO₄ LiFePO₄ LiFePO₄ Ex (ml) organic solution precursors precursors powders 36 100 0.22M Peak 1: small Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 18~24 nm 5~25 nm Length of the Length of the petals: petals: 700~1,800 nm 550~1,400 nm Length of the Length of the plates: plates: 1,500~2,000 nm 700~1,400 nm 37 150 0.22M Peak 1: medium Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 15~20 nm 16~20 nm Length of the Length of the petals: petals: 800~1,800 nm 450~1,300 nm Length of the Length of the plates: plates: 800~2,400 nm 800~2,100 nm 38 100 0.33M Peak 1: medium Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 20~25 nm 12~20 nm Length of the Length of the petals: petals: 800~2,000 nm 650~1,400 nm Length of the Length of the plates: plates: 800~1,900 nm 800~2,000 nm 39 150 0.33M Peak 1: medium Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 12~24 nm 10~20 nm Length of the Length of the petals: petals: 600~1,700 nm 500~1,300 nm Length of the Length of the plates: plates: 800~1,900 nm 900~2,000 nm 40 100 0.44M Peak 1: medium Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 15~20 nm 12~24 nm Length of the Length of the petals: petals: 450~1,500 nm 350~1,300 nm Length of the Length of the plates: plates: 450~2,000 nm 500~1,800 nm 41 150 0.44M Peak 1: medium Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 16~20 nm 12~21 nm Length of the Length of the petals: petals: 550~1,550 nm 600~1,500 nm Length of the Length of the plates: plates: 500~2,600 nm 600~1,900 nm 42 960 0.48M Peak 1: very Petals (with a 3D Petals and plates small structure) and Thickness: Peak 8: plates 20 nm disappeared Thickness: Length of the 14~23 nm petals: Length of the 400~1,750 nm petals: Length of the 600~2,000 nm plates: Length of the 400~2,400 nm plates: 800~2,400 nm Gap between plates: >20 nm 43 67 0.66M Peak 1: large Petals and plates Petals and plates Peak 8: small Thickness: Thickness: 12~20 nm 15~22 nm Length of the Length of the petals: petals: 500~1,500 nm 550~1,500 nm Length of the Length of the plates: plates: 800~1,600 nm 700~1,500 nm

Although the present invention has been explained by its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the present disclosure as hereinafter claimed. 

What is claimed is:
 1. An LiFePO₄ precursor for manufacturing an electrode material of an Li-ion battery, represented by the following formula (I): LiFe_((1-a))M_(a)PO₄  (I) wherein M comprises at least one metal selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Zr, Tc, Ru, Rh, Pd, Ag, Cd, Pt, Au, Al, Ga, In, Be, Mg, Ca, Sr, B, and Nb, 0≤a<0.5, the LiFePO₄ precursor does not have an olivine structure, and the LiFePO₄ precursor is powders constituted by plural flakes; wherein the LiFePO4 precursor comprises an amorphous zone and a crystallized zone.
 2. The LiFePO₄ precursor of claim 1, wherein a content of the amorphous zone is greater than a content of the crystallized zone.
 3. The LiFePO₄ precursor of claim 1, wherein the crystallized zone comprises at least two selected from the group consisting of C₂H₄Li₄O₇P₂·H₂O, Fe₃H₉(PO₄)₆·6H₂O, Fe₂Fe(P₂O₇)₂, FeLiO₂, Li₂Fe₂O₄, FePO₄, C₆H₆FeO₈·2H₂O, FePO₄(H₂O)₂, Li₂O₂, Li, and Fe₂O(PO₄).
 4. The LiFePO₄ precursor of claim 3, wherein the crystallized zone further comprises at least one selected from the group consisting of Fe₃O₄, Fe₃PO₇, Fe₃Fe₄(PO₄)₆ and C₂HLiO₄·H₂O.
 5. The LiFePO₄ precursor of claim 1, which shows an X-ray diffraction pattern having characteristic peaks at near 2θ angles of 19.37°, 21.47°, 24.11°, 25.95°, 32.35°, 35°, 36.46°, and 43.83°.
 6. The LiFePO₄ precursor of claim 5, which shows the X-ray diffraction pattern having further characteristic peaks at near 2θ angles of 18.3°, 28.91° and 30.05°.
 7. The LiFePO₄ precursor of claim 1, wherein the powders has a diameter ranged from 800 nm to 5 μm, a length of each of the plural flakes is respectively ranged from 400 nm to 5000 nm, and a thickness of each of the plural flakes is respectively ranged from 1 nm to 50 nm.
 8. The LiFePO₄ precursor of claim 7, wherein the plural flakes are gathered to from a flower-like shape or laminated to form a shale-like shape.
 9. The LiFePO₄ precursor of 1, wherein the powders are further coated with a carbon layer.
 10. A method for manufacturing an LiFePO₄ precursor for manufacturing an electrode material of an Li-ion battery, comprising the following steps: providing a mixed organic solution, which comprises Li, Fe, and P, wherein the Li contained in the mixed organic solution is derived from a Li-containing precursor or a P and Li-containing precursor, the Fe contained in the mixed organic solution is derived from an Fe-containing precursor or a P and Fe-containing precursor, and the P contained in the mixed organic solution is derived from a P-containing precursor, a P and Li-containing precursor, or a P and Fe-containing precursor; and heating the mixed organic solution under reflux to a predetermined temperature and maintaining the predetermined temperature for a predetermined period to obtain an LiFePO₄ precursor, wherein the LiFePO₄ precursor is represented by the following formula (I): LiFe_((1-a))M_(a)PO₄  (I) wherein M comprises at least one metal selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Zr, Tc, Ru, Rh, Pd, Ag, Cd, Pt, Au, Al, Ga, In, Be, Mg, Ca, Sr, B, and Nb, 0≤a<0.5, the LiFePO₄ precursor does not have an olivine structure, and the LiFePO₄ precursor is powders constituted by plural flakes, wherein the LiFePO₄ precursor comprises an amorphous zone and a crystallized zone.
 11. The method of claim 10, further comprising a step of coating the LiFePO₄ precursor with a carbon source through a milling process to form a carbon layer on the powders.
 12. The method of claim 11, wherein the mixed organic solution is heated under an atmosphere or with an introduced gas flow.
 13. The method of claim 12, wherein the atmosphere or the introduced gas flow comprises one selected from the group consisting of N₂, He, Ne, Ar, Kr, Xe, CO, methane, N₂—H₂ mixed gas, and a mixture thereof.
 14. The method of claim 10, wherein the Li-containing precursor is at least one selected from the group consisting of LiOH, Li₂CO₃, LiNO₃, CH₃COOLi, Li₂C₂O₄, Li₂SO₄, LiCl, LiBr, and LiI; the Fe-containing precursor is at least one selected from the group consisting of FeCl₂, FeBr₂, FeI₂, FeSO₄, (NH₄)₂Fe(SO₄)₂, Fe(NO₃)₂, FeC₂O₄, (CH₃COO)₂Fe, and FeCO₃; the P-containing precursor is at least one selected from the group consisting of H₃PO₄, NaH₂PO₄, Na₂HPO₄, Mg₃(PO₄)₂, and NH₄H₂PO₄; the P and Li-containing precursor is at least one selected from the group consisting of LiH₂PO₄, Li₂HPO₄, and Li₃PO₄; and the P and Fe-containing precursor is at least one selected from the group consisting of Fe₃(PO₄)₂, and FePO₄.
 15. The method of claim 10, wherein the mixed organic solution is heated under atmospheric pressure.
 16. The method of claim 10, wherein an organic solvent in the mixed organic solution is at least one selected from the group consisting of ethylene glycol (EG), diethylene glycol (DEG), glycerol, triethylene glycol (TEG), tetraethylene glycol (TTEG), polyethylene glycol (PEG), Dimethyl sulfoxide (DMSO), and N,N-dimethylmethanamide (DMF).
 17. The method of claim 10, wherein the predetermined temperature is ranged from 105° C. to 350° C., and the predetermined period is ranged from 2 hrs to 20 hrs.
 18. The method of claim 10, wherein the LiFePO₄ precursor shows an X-ray diffraction pattern having characteristic peaks at near 2θ angles of 19.370, 21.47°, 24.110, 25.95°, 32.350, 350, 36.46°, and 43.83°.
 19. The method of claim 18, wherein the LiFePO₄ precursor shows the X-ray diffraction pattern having further characteristic peaks at near 2θ angles of 18.3°, 28.91° and 30.05°.
 20. The method of claim 10, wherein the mixed organic solution further comprises a dispersant.
 21. The method of claim 20, wherein the dispersant is at least one selected from the group consisting of potassium dodecyl sulfate, ammonium dodecyl sulfate, calcium dodecyl sulfate, sodium dodecyl sulfate, copper dodecyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl Sulfate, sodium dodecyl benzene sulfonate, magnesium dodecyl benzene sulfonate, sodium dodecyl sulfonate, magnesium dodecyl sulfonate, sodium decyl sulfonate, and sodium decyl sulfate. 